Monoisopropylphenol or mixtures of monoisopropylphenol with phenol are useful feedstocks for phosphorylation to prepare isopropylated triaryl phosphates. These phosphate ester reaction products are high viscosity fluids having utility as hydraulic fluids and plasticizers.
Isopropylphenols are conventionally prepared by alkylating phenol with propylene in the presence of a Friedel-Crafts catalyst. The isopropylation of phenol yields a statistical distribution of products ranging from mono to di- and higher substituted phenols. Conventional procedures for preparing triaryl phosphates are described in U.S. Pat. Nos. Re. 29,540 and 4,139,487.
The presence of polyisopropyl phenols in phosphorylation feedstocks present several disadvantages. Sterically hindered polyisopropylphenols are more difficult to phosphorylate than monoisopropylphenol. In addition, certain phosphorylated products such as 2,6-diisopropylphenyl/phenyl phosphate are suspected of contributing to unwanted color formation in commercial isopropylphenyl/phenyl phosphate products.
The problem of eliminating unwanted polyisopropyl phenols has been dealt with by distillation of the alkylation reaction product prior to phosphorylation. Alternatively, unwanted polyisopropylphenyl/phenyl phosphates in the triaryl phosphate product have been removed by distillation under reduced pressure. Unfortunately, these prior art methods entail difficult fractionation procedures.